The subject matter disclosed herein relates generally to power electronic modules.
Many gate drivers for power electronic switches such as insulated gate bipolar transistors (IGBTs) and metal oxide semiconductor field effect transistors (MOSFETs) use a desaturation detection technique to determine if a switch is in an over-current state. Upon desaturation detection, the gate driver is then capable of turning off the switch in a controlled and swift manner in order to attempt to prevent switch destruction and damage. A desaturation detection circuit typically comprises a diode including a cathode that is connected to the switch's collector or drain. Current is injected into the desaturation detection diode using an appropriate source, and the emitter or source serves as the return path.
Typical desaturation detection diodes have reverse recovery times on the order of one hundred nanoseconds and current ratings on the order of one ampere. The reverse recovery of such diodes is designed to be as small as possible and in the worst case should typically be at least on par with the rate of the total switching time of the switch. Because current on the order of ten milliamperes to twenty milliamperes is injected into the switch, the current rating of such desaturation detection diodes generally needs only be on the order of fifty milliamperes. The voltage rating of such diodes must be at least as high as the voltage rating of the switch. For high voltage switches (with two examples being 1200V and 1700V switches), diodes are typically connected in series. Series coupling may lead to added problems of matching the intrinsic parameters to ensure equal sharing of the blocking voltage, particularly during switching transients. Silicon carbide diodes typically can withstand these high voltages and have very low to negligible reverse recovery times. However, silicon carbide diodes typically have current ratings that are greater than five amperes and are often only available in bulky packages.
Conventional desaturation detection approaches are designed to integrate the desaturation detection diode within the gate driver circuit and include high voltage cables between the switch and the gate driver circuit. It would be desirable to have a desaturation detection system with improved reliability and reduced parasitic inductance. It would also be desirable to eliminate the conventional high voltage cable that carries desaturation signals between the gate driver and the power switch module.